The need for systems that can deliver a drug at a controlled rate to a variable environment (e.g. gastrointestinal tract) of use over a specified period of time is well established. The use of novel, charged, water-insoluble, non-diffusible resinous powders to modulate the pH dependency of drug release from osmotically sensitive devices with rate-controlling microporous walls that are permeable to both water and dissolved solutes has not been disclosed in the prior art and represents an advance in drug delivery technology and device composition. For example, devices for the controlled and continuous delivery of an active agent made from microporous materials are known to the prior art. Generally, the agent is embedded in or surrounded by the material and its release therefrom often is adversely influenced by external conditions. For example, U.S. Pat. No. 2,846,057 discloses a device consisting of a porous cellophane wall surrounding sodium fluoride that is released by water flowing into the pores to dissolve and leach it from the device. Controlled release is hard to obtain with this device because release is governed by external conditions and not by the device. That is, the amount of fluoride released changes with the rate of flow of water, with higher rates increasing the amount released, and lower rates decreasing the amount released over time. Similarly, U.S. Pat. No. 3,538,214 discloses a device consisting of drug coated with a film of water-insoluble plastic containing a modifying agent that is soluble at a certain pH. When this device is in the gastrointestinal tract, the modifying agent is partially or fully dissolved from the film by gastrointestinal fluid to form a porous film. This lets fluid through the film to dissolve the drug and leach it outwards through the pores into the tract. Controlled release is difficult to achieve with this device because the selection of the modifying agent is based on the unknown acid and alkaline state of the gastrointestinal tract which concomitantly influences pore formation and the exposure of drug to fluid. A similar device is disclosed in U.S. Pat. No. 2,928,770. The device of this patent consists of an outer layer of drug coated onto a porous material having its pores filled with a softened wax that is supposedly removed in the gastrointestinal tract by the alimentary fluid. This device cannot be relied on for controlled release because it too requires in situ pore formation which is dominated by unregulated external conditions and not by the device. The use of pore formers in substantially water impermeable polymers is disclosed in J. Pharm. Sci. 72, p. 772-775 and U.S. Pat. Nos. 4,244,941; 4,217,818; and 3,993,072. These devices release the core components by simple diffusion. U.S. Pat. No. 3,957,523 discloses a device which has a pH sensitive pore former in the device wall. U.S. Pat. Nos. 4,309,996; 4,320,759; 4,235,236 disclose layered devices with a microporous coating containing a drug layer and a swelling polymer layer acting as the driving force for delivery of agents. U.S. Pat. Nos. 4,256,108; 4,160,452; 4,200,098 and 4,285,987 disclose devices with pore formers in one of multiple wall layers. These devices contain a drilled hole for the release of core components through rate controlling semipermeable membranes that are substantially impermeable to dissolved drugs and other solutes. The use of charged resins to modulate drug release from the above devices was not disclosed. U.S. Pat. No. 4,221,778 discloses ion exchange resin drug complexes as delivery devices where the resin and drug carry opposite charges and microporous coats and osmotic factors are not included: drug release is actuated by exchange of the drug with another ion which dislodges the drug from the resin.